【正文】 e ? Plug valve ? Adjusting valve ? Cutoff valve ? Threeway valve ? Handoperating valve ? Safety valve ? Electricoperated valve ? Pneumaticoperated valve Connecting manner ? Flange connection ? Threaded connection ? Clamp connection ? Welding connection ? 41 Chapter 2. Valves A device that places a movable metal gate in the path of a process flow. 1. Gate valves Bon 機(jī)罩 Yoke 機(jī)架 The typical gate valve consists of a gate, body, seating area, stem, bon, packing, stuffing box, packing gland, and hand wheel. The gates are sized to fit the inside diameter of a pipe. ? 42 Chapter 2. Valves Very little restriction occurs when it is in the open position. 1. Gate valves ? Size: from ” to several feet. ? Path: from “ wide open” to “ pletely shut” . ? Should not be used to throttle flow. The gate can be wedge shaped or may consist of parallel discs. The gate is placed directly in the path of a process flow when it is shut and is lifted pletely out of the way when open. ? 43 Chapter 2. Valves Gate valves The body is the largest part of the valve. The body can be connected to the process piping in three ways: flanges, threaded, or welding. The seating consists of two fixed surfaces or rings inside the body of the valve that the gate closes against to stop flow. The seating area falls into two categories: replaceable or fixed. The stem is a long, slender shaft attached to the gate, bushing, or wheel. When the hand wheel is turned, it transmits rotational energy to the stem, causing it to rise to open or lower to close. The bon provides a housing for the gate or disc when it is lifted out of the process flow. It is attached to the body permanently by welding or temporarily by threading or bolts. ? 44 Chapter 2. Valves 2. Globe valves ?Globe valves are the second most mon used in industry. ?A globe valve places a movable metal disc in the path of a process flow. ?This type of valve is most monly used for throttling service. ?The disc is designed to fit smugly into the seat and stop flow. ?Process fluid enters the globe valve and is directed through a 90o turn to the bottom of the seal and disc. ? 45 Chapter 2. Valves 2. Globe valves ?Globe valves must be installed properly to work well. ?If the valves is installed backward it will tend to wear unevenly and push the flowcontrol element down. ? 46 Chapter 2. Valves 2. Globe valves The typical globe valve consists of: disc body seating area stem bon packing Stuffing box Packing gland Hand wheel ? 47 Chapter 2. Valves 2. Globe valves The disc is attached to the stem in three ways: Slip joint Threading Onepiece manufacturing The disc can be classified as plug, ball, position, or needle shape. ? 48 Chapter 2. Valves 3. Ball valves ?The hollow ball rotates into the open or closed position. ?A ball valve does not lift the flowcontrol device out of the process stream. ?Ball valves provide very little restriction to flow and can be fully opened with a quarter turn on the valve handle. ?In the closed position, the port is turned away from the process flow. In the open position, it lines up perfectly with the inner diameter of the pipe. ? ?Ball valves take their name from the ball shaped, movable element in the center of the valve. 49 Chapter 2. Valves 3. Ball valves ?Ball valves are not designed for excessive temperatures. ?It should not be used for throttling service. ?Ball valves do not generally seal as well as globe valves in highpressure service. ?Some ball valves (multiport valves) are designed with multiple ports, so an operator can switch fluid sources without stopping flow. ? ?The ball valves only require onequarter turn on a handle. 50 Chapter 2. Valves 4. Check valves ?Flow lifts the disc and keeps it lifted until flow stops or reverses. ?A typical check valve design is the swing check, which has a hinged disc that slams shut when flow reverses. ?A check valves is designed to prevent reverse flow and to avoid possible contamination